1. Field of the Invention
The present invention concerns journal bearings which are resiliently mounted to optimize load capacity for varying operating conditions.
2. Description of Related Art
Bearings may be classified broadly into three main categories: Hydrodynamic sliding bearings, roller bearings, and hydrostatic bearings. Each of the aforementioned types of bearings have problems associated with load-carrying capacity, accuracy, lubricant requirements due to friction, wear and fatigue.
Hydrodynamic sliding bearings typically operate so that the bearing surfaces which slide against each other are rigid and lubricant in the form of a film between the bearing surfaces, which is under hydrodynamic pressure generated by the motion of the bearing itself, serves to support the bearing surfaces in a spaced relation to permit relative movement of the bearing members without wear. These hydrodynamic sliding bearings may be characterized as a rigid isoviscous sliding device wherein a stationary sleeve is used to support a rotatable member such as a shaft in a stationary housing. A lubricant is provided between the interengaging cylindrical surfaces of the sleeve and shaft, whereby upon relative rotation of the bearing surfaces, the hydrodynamic lubricant pressure builds up to support the shaft.
Rolling member bearings characteristically involve bearing surfaces which are capable of rolling on each other, and lubricant being disposed between the bearing surfaces. Rolling member bearings include inner and outer rings which are spaced apart to define an annular space for a plurality of rolling members such as balls or rollers.
In hydrostatic sliding bearings, the rotating shaft is supported or floated on a body of pressurized fluid lubricant, either gaseous or liquid. Such assemblies require complex lubricant feed systems.
The present invention provides an improved hydrodynamic sliding bearing, wherein the stresses or loads on the bearings are more evenly distributed between the bearing pads. Examples of hydrodynamic sliding bearings are described in patents to Greene (U.S. Pat. No. 3,930,691), Ide (U.S. Pat. Nos. 4,496,251 and 4,515,486), as well as Gardner (U.S. Pat. No. 4,403,873).
Greene describes a hydrodynamic sliding bearing which includes a bearing pad having a metal-elastomer laminated structure which is arcuately curved with the center of curvature of the arc being in the direction of the opposing member of the bearing. The structure of the bearing pads permits swinging thereof to produce a wedge converging in the direction of movement of the moving member, such as a shaft. The bearing pad includes face and base sections which are bonded to a metal-elastomer laminant. This pad may be used with either journal or thrust bearings.
Ide '486 describes an elastomeric supported hydrodynamic bearing which consists essentially of a number of bearing pads, each having a face member and a support member that are separated and bonded together by an elastomeric material. The face member having a load engaging surface, and its back surface having at least one arcuate portion to provide a point of inflection which opposes an identical arcuate surface providing another point of inflection located on the support member.
Ide '251 describes a hydrodynamic bearing wherein the bearing surfaces are segmented into a plurality of pads that rockingly displace themselves to form a wedge shape converging in the direction of motion with a relatively moving part. The pads are each supported in a bearing housing or support portion by a plurality of webs which are integral with the pad and the housing or support portion, which allow the pads to rock by deflection of the webs.
Gardner describes a hydrodynamic thrust bearing with tilting pads. The thrust bearing pads are provided with a radically extending rib on a side that is remote from the surface of the pad that interfaces with the shaft collar. Each pad is supported on a disk that has a planar surface on which the rib of a pad bearing and each disk has a spherical surface opposite from its planar surface. The disks are supported on leveling links that have angular, but flat, wings extending in opposite circumferential directions. The links have a radial hole and are supported for pivoting on a fixed pin about an axis.
Essentially, each of the aforementioned hydrodynamic bearings is mounted in such a way that it can move to permit the formation of a wedge-shaped film of lubricant between the relatively moving parts. The pads are displaced through a swing-type motion about a center located in front of each pad's surface, and bearing friction tends to open the wedge.
Each of these journal and thrust-type hydrodynamic bearings has a common problem with load distribution among the pads. The shore or bearing pad situated directly below the load has the greatest stress or highest load. Each additional bearing pad adjacent to the load carrying pad carries less and less of a load, such that the pads situated 90 degrees from the load carrying pad carry no load. This uneven load distribution among the pads results in some bearing pads having higher loads, greater stresses, and/or increased wear and fatigue.